The aims of this project are based on three hypothesis. Hypothesis 1 is that the opioid delta receptor may exist as subtypes. An antisense strategy will be employed in NG 108-15 cells, in primary DRG cultures and in an antinociceptive model in vivo. Antisense oligodeoxynucleotide (ODN) "knock-down" of delta receptors in NG108-15 cells will be studied using ODNs directed at the DOR-1 clone and at a conserved sequence in the opioid mu, delta and kappa receptors (conserved opioid receptor; COR). Cellular uptake and ODN translocation, time-course, concentration-dependence and inhibition of the delta receptor expression will be determined with fluorescence microscopy and radioligand binding; control ODN sequences will be emphasized. In DRG cultures DOR or COR antisense ODN will be used to evaluate ODN uptake and morphological distribution and to validate the DOR ODN selectivity against delta mu and kappa receptors. In rats, DOR/COR ODNs will be used to elucidate the distribution of spinal ODNs and "knock-down" of opioid receptors and possible differential sensitivity of putative delta subtype selective agonists (but not mu or kappa agonists), to DOR-1 antisense ODN effects as well as time-course and recovery of the antinociceptive effect. Hypothesis 2 is that activation of supraspinal opioid delta receptors will produce antinociception not necessarily dependent on the descending pathway characterized for opioid mu receptor agonists. Localized microinjection of opioid subtype selective agonists and antagonists into selected supraspinal loci will be employed to establish receptor selective antinociceptive activity. The involvement of descending pathways following activation of confirmed supraspinal delta antinociception will be studied by examining suppression of nociceptive induced behavior and c-FOS expression in the spinal cord in control rats, or in animals with lesions of the dorsolateral funiculus (DLF). Hypothesis 3 is that activation of both supraspinal and spinal opioid delta receptors will result in a synergistic antinociceptive effect. Analysis of antinociception elicited by supraspinal/spinal co-administration of subtype-selective agonists in a fixed-ratio paradigm with isobolographic methods will be used. These experiments should yield significant new information about the role of the delta receptor in nociception and the bossibility of subtypes of this receptor in vitro and in vivo.